The invention relates to a method and a pump apparatus for the generation of an adjustable, substantially constant volume flow of a fluid and to the use of this method.
The necessity exists of transporting a fluid in a metered manner in many industrial processes and in the conduct of numerous methods; i.e. a substantially constant volume flow of the fluid should be forwarded in the sense that the quantity of fluid forwarded per unit of time is constant. An example which can be given here is chemical-mechanical polishing (CMP) processes such as are used in the semi-conductor industry. In such processes, a suspension, which is usually called a slurry and is typically made up of very fine solid particles and a liquid, is brought onto a rotating wafer and serves there for the polishing or lapping of the very fine semi-conductor structures. In this respect, it is necessary for the suspension (slurry) to be applied to the wafer surface with a constant, adjustable volume flow, i.e. in a metered manner.
In other processes, for example the application of photosensitive resist onto the wafer, it is necessary to transport a metered quantity of fluid, which can as a rule be realized by the transportation of a constant volume flow over a predetermined time.
Volumetric pumps such as peristaltic pumps, gear pumps, piston pumps and diaphragm pumps are used nowadays for such metered forwarding. Such volumetric pumps have the characteristic that they forward a well-defined quantity of fluid per working cycle. With a piston pump, for example, the fluid volume forwarded per stroke is fixed by the piston area and the piston stroke. A constant volume flow can thus be generated because the same volume of fluid is forwarded with each stroke of the piston.
Volumetric pumps, however, have characteristics which can prove to be disadvantageous in some applications, for example they generally generate pulsating fluid flows. The pressure fluctuations associated with this can prove to be very disturbing. They can also facilitate deposits or agglomeration of particles. Moreover, with special liquids, such as with the already mentioned slurry suspensions, the solid particles can result in substantial damage to the pump due to abrasion, in particular to the sealing components between the suction side and the pressure side. For instance, leaks can occur due to the abrasive particles, for example, along the piston in a piston pump, as the piston rings and/or the cylinder wall are damaged.